1. Field of the Invention
The invention relates to device for encoding digital video signals which are representative of the luminance or the chrominance of a given number of pixels of a picture divided into blocks, comprising particularly a correlation reduction circuit, a normalization circuit, a quantization circuit, an encoding circuit as well as a rate control circuit which receives the output signals from the encoding circuit at a variable rate and supplies, on the one hand, rate control signals applied to the normalization circuit and, on the other hand, encoded signals at a constant rate at the output of the encoding device.
With a view to their transmission or recording, the digitization of television signals is a solution which is extremely useful in the case of connections where the disturbing noise is particularly significant, notably in connections by way of satellite. A television image comprises a very large quantity of information components whose digital representation is expressed by a high rate. By sampling the components of the television signal at a frequency satisfying the Shannon condition and by using a uniform quantization at 256 levels, the direct digitization of the luminance and chrominance components at frequencies of 13.5 and 6.75 MHz, respectively, imposed by the standards, would contribute in effect to a rate of 216 Meb/s. This rate is quite prohibitive, notably in the case of magnetic recording devices for consumer use. The use of rate reduction techniques is thus necessary and is all the more realizable as the image exhibits a relatively considerable redundancy.
2. Description of the Related Art
A device as mentioned in the opening paragraph is described in Patent Application WO 88/04508. In this device the normalization is ensured by associating with each picture block a classification factor of this block in a particular class characterized by a specific criterion. This specific criterion is unique and is based on a classification of blocks in accordance with the largest or smallest number of details which they comprise in accordance with one or the other of the spatial dimensions of the picture. The encoding is subsequently adjusted as a function of the classification thus performed.